Previous art for making a furan polymer impregnated wood by impregnating wood with a furfuryl alcohol solution and then polymerizing the furfuryl alcohol inside the wood, producing a dark brown wood polymer composite in treated zones, have been performed in different ways, as disclosed hereinafter.
1. Initiators
In the oldest method, initiators were water-soluble salts, particularly zinc chloride. The salt was dissolved in water and then the solution was added to the furfuryl alcohol. Salt weight was approximately 5% of furfuryl alcohol weight. This mixture was then impregnated into wood and polymerized using heat. As impregnation took place, the water and salt was retained by the wood near the surface. Furfuryl alcohol reaching deeper into the wood was therefore depleted of initiator and did not cure well. Therefore, this method was restricted to short or thin pieces of wood.
A newer method used a two-stage process. First, a zinc chloride solution in water was made. This was impregnated into wood and the wood dried. The amount of dried salt was approximately 5% of the calculated amount of furfuryl alcohol which would be impregnated in the following step. Next the wood was impregnated with furfuryl alcohol. It was then cured using heat. A uniform material was formed by this method, but it required 2 impregnation and drying stages.
2. Size of Material
For the older method, thin sections and short lengths of wood were required for the reasons mentioned above. Lumber-sized material had strong colour and density gradients when so treated, with the darker and denser material near the surfaces of the treated wood. In the well-treated zones near surfaces (or in small pieces), treated densities were in the range of 0.9 g/cc to 1.15 g/cc, while in the interior, the density approached that of the parent wood, and uncured furfuryl alcohol was usually present.
The newer method was not size-restricted like the older one, but the method took a great deal longer since drying in the first stage required care to prevent splitting and warping.
3. Colour of Material
Because of the gradients using the older method mentioned above, colour of the material varied with depth from surfaces. Machining or sanding therefore exposed material of lighter colour, with the colour varying with distance from the surface. The newer method had excellent colour throughout.